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Date: Thu, 3 Dec 2015 21:51:03 +0100
From: Rasmus Villemoes <linux@...musvillemoes.dk>
To: Andrew Morton <akpm@...ux-foundation.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Kees Cook <keescook@...omium.org>,
Martin Kletzander <mkletzan@...hat.com>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>,
Joe Perches <joe@...ches.com>,
Maurizio Lombardi <mlombard@...hat.com>,
Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits
Maurizio Lombardi reported a problem [1] with the %pb extension: It
doesn't work for sufficiently large bitmaps, since the size is stashed
in the field_width field of the struct printf_spec, which is currently
an s16. Concretely, this manifested itself in
/sys/bus/pseudo/drivers/scsi_debug/map being empty, since the bitmap
printer got a size of 0, which is the 16 bit truncation of the actual
bitmap size.
We do want to keep struct printf_spec at 8 bytes so that it can
cheaply be passed by value. The qualifier field is only used for
internal bookkeeping in format_decode, so we might as well use a local
variable for that. This gives us an additional 8 bits, which we can
then use for the field width.
To stay in 8 bytes, we need to do a little rearranging and make the
type member a bitfield as well. For consistency, change all the
members to bit fields. gcc doesn't generate much worse code with these
changes (in fact, bloat-o-meter says we save 300 bytes - which I think
is a little surprising).
I didn't find a BUILD_BUG/compiletime_assertion/... which would work
outside function context, so for now I just open-coded it.
[1] http://thread.gmane.org/gmane.linux.kernel/2034835
Reported-by: Maurizio Lombardi <mlombard@...hat.com>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Joe Perches <joe@...ches.com>
Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
lib/vsprintf.c | 41 +++++++++++++++++++++--------------------
1 file changed, 21 insertions(+), 20 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 63ca52366049..01c3aa638582 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -380,13 +380,13 @@ enum format_type {
};
struct printf_spec {
- u8 type; /* format_type enum */
- u8 flags; /* flags to number() */
- u8 base; /* number base, 8, 10 or 16 only */
- u8 qualifier; /* number qualifier, one of 'hHlLtzZ' */
- s16 field_width; /* width of output field */
- s16 precision; /* # of digits/chars */
-};
+ unsigned int type:8; /* format_type enum */
+ signed int field_width:24; /* width of output field */
+ unsigned int flags:8; /* flags to number() */
+ unsigned int base:8; /* number base, 8, 10 or 16 only */
+ signed int precision:16; /* # of digits/chars */
+} __packed;
+extern char __check_printf_spec[1-2*(sizeof(struct printf_spec) != 8)];
static noinline_for_stack
char *number(char *buf, char *end, unsigned long long num,
@@ -1641,6 +1641,7 @@ static noinline_for_stack
int format_decode(const char *fmt, struct printf_spec *spec)
{
const char *start = fmt;
+ char qualifier;
/* we finished early by reading the field width */
if (spec->type == FORMAT_TYPE_WIDTH) {
@@ -1723,16 +1724,16 @@ precision:
qualifier:
/* get the conversion qualifier */
- spec->qualifier = -1;
+ qualifier = 0;
if (*fmt == 'h' || _tolower(*fmt) == 'l' ||
_tolower(*fmt) == 'z' || *fmt == 't') {
- spec->qualifier = *fmt++;
- if (unlikely(spec->qualifier == *fmt)) {
- if (spec->qualifier == 'l') {
- spec->qualifier = 'L';
+ qualifier = *fmt++;
+ if (unlikely(qualifier == *fmt)) {
+ if (qualifier == 'l') {
+ qualifier = 'L';
++fmt;
- } else if (spec->qualifier == 'h') {
- spec->qualifier = 'H';
+ } else if (qualifier == 'h') {
+ qualifier = 'H';
++fmt;
}
}
@@ -1789,19 +1790,19 @@ qualifier:
return fmt - start;
}
- if (spec->qualifier == 'L')
+ if (qualifier == 'L')
spec->type = FORMAT_TYPE_LONG_LONG;
- else if (spec->qualifier == 'l') {
+ else if (qualifier == 'l') {
BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG);
spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN);
- } else if (_tolower(spec->qualifier) == 'z') {
+ } else if (_tolower(qualifier) == 'z') {
spec->type = FORMAT_TYPE_SIZE_T;
- } else if (spec->qualifier == 't') {
+ } else if (qualifier == 't') {
spec->type = FORMAT_TYPE_PTRDIFF;
- } else if (spec->qualifier == 'H') {
+ } else if (qualifier == 'H') {
BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE);
spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN);
- } else if (spec->qualifier == 'h') {
+ } else if (qualifier == 'h') {
BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT);
spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN);
} else {
--
2.6.1
--
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